Remove dead code
[luaConfigFile] New function for popup message generation
[luaConfigFile] Rename addWidget function to init
On object creation defer widget text generation

When a text widget is created, it's text needs to be generated quickly in order
to avoid a "popup" glitch. It used to be done by calling the update method
irecly in the initializor. This method implies that awesome will fail to load
if any update function throws an error.

Defer execution by sending a signal emulate a timer timeout.
[rc.lua]Remove useless log
[tb_volume] Fix typo
Cache widget text to avoid unnessary update

Useless widget text update were responsible for a 2% cpu usage per update :(